The present invention relates to curable casting resin compositions that may be used in the formation of a variety of materials, including, but not limited to, lenses, camera optics, prisms and video disks.
Ophthalmic lenses produced in industry must meet certain requirements for their intended use. For example, as mandated by the U.S. Food and Drug Administration (FDA), ophthalmic lenses should have sufficient impact resistance in addition to having acceptable optical properties. The performance and quality of lenses has been improved with the addition of scratch resistant coatings, anti-reflective (AR) coatings, UV protection and lens materials with high refractive index and high Abbe value. Further, lens cosmetics have also been improved by aspheric and progressive lens designs.
Many efforts in formulating UV curable casting resin compositions have been made to produce thinner lenses having a high refractive index. By increasing the refractive index of the lens materials, the edge thickness of minus-prescripted lenses and center thickness of plus-prescripted lenses is reduced. Reducing edge and center thicknesses of lenses provides functional advantages such as lighter weight and better cosmetics. Representative examples of UV curable casting resin formulations for forming lenses are described below.
U.S. Pat. No. 4,306,780 discloses high index lens formulations comprising three types of materials: (a) 3-70% of one or more of ethoxylated bisphenol A di(meth)acrylates, (b) 30-97% of high index reactive diluents, and (c) 0-67% of low index methacrylate(s). Based on the information provided in the patent disclosure, low impact resistance and inferior thermomechanical properties are expected from the high refractive index lenses made from these formulations because of the large amount of reactive diluent used in the formulations.
U.S. Pat. Nos. 5,442,022 and 5,545,828 disclose lens formulations comprising (a) at least 50% of a monomer or mixture of monomers having formula (A), (b) 0-50% of one or more mono- or poly-functional vinyl or (meth)acrylate comonomers, and (c) 0.5 to 15% of allyl alcohols or their derivatives. Lenses produced from a homopolymer of formula (A) have a refractive index greater than or equal to 1.55; however, these lenses have an inferior physical/cosmetic property in that they are very yellow in color. Further, although incorporating components (b) and (c) into the lens formulations reduces the yellowness of the resulting lens, lens formulations comprising components (a), (b) and (c) produce lenses having an undesired lower refractive index. Also, the typical time for thermally curing these lens formulations is more than 20 hours. A curing time of this length drastically reduces lens manufacturing efficiency. The formula disclosed in U.S. Pat. Nos. 5,442,022 and 5,545,828 may be represented by: 
wherein R1 and R2 are H or C1-C6 alkyl; X is O, S, SO2, CO2, CH2, CHxe2x95x90CH or C(H3)2; and m+n is 0-10.
U.S. Pat. No. 5,373,033 discloses casting resin formulations with (a) 5-60% of polyoxyalkylene glycol di(meth)acrylates, (b) 10-60% of bisphenol-based monomers having the general formula (B) and (c) 2.5-20% of urethane (meth)acrylates. The impact resistance for these formulations was not reported; however, the impact resistance is expected to be improved due to the introduction of urethane (meth)acrylates into the formulation. The reported refractive index of the cured sample is no more than 1.55. The formula disclosed in U.S. Pat. No. 5,373,033 may be represented by: 
wherein R, is H, CH3 or CH2CH3; R2 is H, CH3 or CH2CH3; R3 is H, CH3 or OH; R4 is H, CH3 or CH2CH3; X is a halogen (preferably Cl, Br or I) or hydrogen; and n is 0-8.
The lenses produced using these high index materials represented above by formulae (A) and (B) may have one or more of the shortcomings mentioned above. For instance, the high index materials of formulae (A) and (B) are mixed with at least 2 other types of materials to adjust index, viscosity and impact resistance in order to obtain lenses with reasonable overall properties. However, the impact resistance and themomechanical properties of these lenses are expected to be inferior. Further improvement is needed to formulate high index casting resins capable of producing much higher quality lenses by developing new high index materials.
Steps have also been taken to impart UV protection in lenses produced from the aforementioned formulations. These steps are typically accomplished by dipping the cured lenses in a UV tinting bath in separate steps. However, the UV tinting process tends to introduce yellowness into the lens and increases the cost of lenses.
Thus, there is a need to formulate a low viscosity casting resin formulation that is curable in a short amount of time and produces lenses having a high refractive index and excellent impact resistance. In particular, there is a need for high impact resistance in lenses having a center thickness of 1 mm. That way, true thin and light high refractive index lenses having the required impact resistance can be produced. Further, there is a need for lenses having at least 99% inherent UVA protection up to 380 nm. Having inherent UV protection eliminates additional UV tinting process steps and the resulting yellowness in the lens. Lastly, a casting resin composition of low viscosity enables easier processing in the mold-filling stage and prevents flow lines and bubbles in the cured lenses.
The present invention is generally directed to a low viscosity casting resin composition that can be cured under radiation to produce high refractive index lenses with excellent impact resistance and inherent UV protection. Moreover, the present invention is directed to a curable casting resin composition having a UV absorber therein to provide more than 99% inherent UVA protection.
In one aspect, the present invention is directed to a high refractive index composition comprising:
a core resin mixture comprising
(i) a first compound and/or a mixture thereof having the formula (I): 
xe2x80x83wherein the average value of n and nxe2x80x2 independently are 0-30, R1-R4 independently represent H or C1-C6 alkyl, X is O, S, SO2, CO2, CH2, CHxe2x95x90CH, C(CH3)2 or a single bond, and y1-y8 independently represent H, OH, halogen, mercaptan and derivatives thereof or C1-C4 alkyl,
(ii) a second compound is a poly(ethylene glycol) di(meth)acrylate anchor a mixture thereof, having the formula (II): 
xe2x80x83wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) a reactive diluent comprising, 1,6-hexanediol di(meth)acrylate, trimethyloipropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl benzoate, styrene, divinyl benzene or a mixture thereof;
the mixture having 40-100 parts by weight of the composition of component (i), up to 30 parts by weight of the composition of component (ii) and up to 30 parts by weight of the composition of component (iii), based on the total parts by weight of the combined components (i), (ii) and (iii) equaling 100.
In another aspect, the composition of the present invention comprises
(a) a core resin mixture comprising:
(i) 40 to 100 parts by weight of a first compound and/or a mixture thereof, based on the total parts by weight of the core resin equaling 100, having the formula (I): 
xe2x80x83wherein the average value of n and nxe2x80x2 independently are 0-30, R1-R4 independently represent H or C1-C6 alkyl, X is O, S, SO2, CO2, CH2, CHxe2x95x90CH, C(CH3)2 or a single bond, and y1-y8 independently represent H, OH, halogen, mercaptan and derivatives thereof or C1-C4 alkyl,
(ii) up to 30 parts by weight of a second compound of a poly(ethylene glycol) di(meth)acrylate and/or a mixture thereof, based on the total parts by weight of the core resin equaling 100, having the formula (II): 
xe2x80x83wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) up to 30 parts by weight of a reactive diluent comprising, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl benzoate, styrene, divinyl benzene or a mixture thereof,
(b) up to 2 parts by weight of an ultraviolet absorber per 100 parts by weight of the core resin; and
(c) up to a combined total of 3 parts by weight of an additive per 100 parts by weight of the core resin.
The present invention is also directed to a method of forming a cured article from the compositions of the present invention. The method comprises the steps of: (a) filling a mold with a high refractive index curable resin composition of the present invention; (b) curing the composition of step (a) by exposure to a radiation source thereby forming a cured article; (c) demolding the cured article; and (d) annealing the cured article. Preferably, the article is a lens.
The present invention may be understood more readily by reference to the following detailed description of particular embodiments of the invention and the specific examples included therein.
Before the present compositions and methods are disclosed and described, it is to be understood that this invention is not limited to specific synthetic methods or to particular formulations, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.
In this specification and in the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings.
The singular forms xe2x80x9ca,xe2x80x9d xe2x80x9canxe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the context clearly dictates otherwise. xe2x80x9cHigh refractive indexxe2x80x9d or xe2x80x9chigh indexxe2x80x9d when used in reference to the polymer formed from a casting resin composition means that the cured polymer preferably has a refractive index (RI) of at least 1.51 to 1.57, and more preferably of at least 1.53 to 1.56.
xe2x80x9cInherent UV protectionxe2x80x9d when used in reference to the polymer formed from a casting resin composition of this invention means that the cured polymer having a WV absorber therein preferably has ultra violet (UV) blockage of 100% UVB and at least 95% and more preferably of at least 99% UVA (up to 380 nm).
xe2x80x9cCore resinxe2x80x9d when used in reference to a curable casting resin composition of this invention refers to a resin having the combination of an ethoxylated bisphenol A di(meth)acrylate monomer and/or mixtures thereof and a reactive diluent.
The term xe2x80x9cethoxylated bisphenol A di(meth)acrylatexe2x80x9d refers to itself as well as its derivatives as outlined in formula (I) with n=nxe2x80x2xe2x89xa00. It is also referred to as EBADMA.
The term xe2x80x9c(meth)acrylatexe2x80x9d or xe2x80x9c(meth)acrylate mixturesxe2x80x9d when used in reference to the curable casting resin composition of this invention refers to an acrylate monomer wherein the monomer or monomer mixture may be a methacrylate or acrylate.
The term xe2x80x9creactive diluentxe2x80x9d refers to a radically polymerizable monomer used to reduce the concentration of the ethoxylated bisphenol A di(meth)acrylate and/or mixtures thereof to achieve the presently described desirable and beneficial effects, especially low viscosity, high refractive index and/or better thermomechanical properties.
The term xe2x80x9cgrid lampxe2x80x9d refers to a radiation source from phosphor coated low pressure mercury lamp.
The amount of reactive diluent used in the core resin varies according to the types and amounts of ethoxylated bisphenol A di(meth)acrylate used, and is used in an amount to effect a high refractive index without sacrificing a high impact resistance imparted to the resulting cured substrate or lens.
The present invention is generally directed to a low viscosity, curable casting resin composition for producing articles having a high refractive index, high impact strength and inherent UV protection. The casting resin compositions are radiation and/or thermally curable. More preferably, the casting resin compositions of this invention are UV radiation curable.
In one embodiment, the high refractive index curable composition comprises a core resin mixture comprising:
a first compound and/or a mixture thereof having the formula (I): 
xe2x80x83wherein the average value of n and nxe2x80x2 independently are 0-30, R1-R4 independently represent H or C1-C6 alkyl, X is O, S, SO2, CO2, CH2, CHxe2x95x90CH, C(CH3)2 or a single bond, and y1-y8 independently represent H, OH, halogen, mercaptan and derivatives thereof or C1-C4 alkyl,
(ii) a second compound is a poly(ethylene glycol) di(meth)acrylate and/or a mixture thereof, having the formula (II): 
xe2x80x83wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) a reactive diluent comprising, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl beonoate, styrene, divinyl benzene or a mixture thereof;
the mixture having 40-100 parts by weight of the composition of component (i), up to 30 parts by weight of the composition of component (ii) and up to 30 parts by weight of the composition of component (iii), based on the total parts by weight of the combined components (i), (ii) and (iii) equaling 100.
The di(meth)acrylate of formula I may preferably be present at least 40 parts, and most preferably at least 45 parts, by weight of the total composition.
The poly(ethylene glycol) di(meth)acrylate of formula II may preferably be present at 5-30 parts, more preferably 10-25 parts, and most preferably at 15-25 parts by weight of the total composition.
In formula I: n and n preferably are 0-15, more preferably 0-8, and even more preferably at least 1; one or both of R1 and R4 preferably represent H or CH3, and more preferably CH3; one or both of R2 and R3 preferably represent H; X preferably represents C(CH3)2; and/or one or more of y1-y8 preferably represent H.
In formula II: m preferably is at least 2, more preferably 3 or more, and even more preferably 4 or more; R5-R7 preferably independently represents H or C1-C6 alkyl, more preferably, R5 and R7 independently represents CH3 and R6 is H.
The degree of alkoxylation in formula I and/or II can generally be varied to give the high refractive index and superior impact resistance of the invention throughout the scope of compounds covered by the generic structure for formula I and/or II. The impact resistance of the cured compositions of this invention may, of course, vary. The resin preferably gives a composition upon polymerization and curing that passes the FDA required drop ball #1 impact resistance test, more preferably passes the drop ball #10 test, and even more preferably passes the drop ball #13 test. High impact resistance, for purposes of defining the cured compositions of this invention, means at least passing the drop ball #1 impact resistance test.
In a second embodiment, the high refractive index curable composition comprises a core resin mixture comprising:
(i) a first compound and/or a mixture thereof having the formula (I): 
xe2x80x83wherein the average value of n and nxe2x80x2 independently are 0-30, R1 and R4 independently represent H or CH3, R2 and R3 are H, X is C(CH3)2 and y1-y8 are H,
(ii) a second compound is a poly(ethylene glycol) di(meth)acrylate and/or a mixture thereof, having the formula (II): 
xe2x80x83wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) a reactive diluent comprising, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl bemzoate, styrene, divinyl benzene or a mixture thereof;
the mixture having 40-100 parts by weight of the composition of component (i), up to 30 parts by weight of the composition of component (ii) and up to 30 parts by weight of the composition of component (iii), based on the total parts by weight of the combined components (i), (ii) and (iii) equaling 100.
In another aspect, the composition of the present invention comprises
(a) a core resin mixture comprising
(i) 40 to 100 parts by weight of a first compound and/or a mixture thereof, based on the total parts by weight of the core resin equaling 100, having the formula (I): 
xe2x80x83wherein the average value of n and nxe2x80x2 independently are 0-30, R1-R4 independently represent H or Cl-C6 alkyl, X is O, S, SO2, CO2, CH2, CHxe2x95x90CH, C(CH3)2 or a single bond, and y1-y8 independently represent H, OH, halogen, mercaptan and derivatives thereof or C1-C4 alkyl,
(ii) up to 30 parts by weight of a second compound of a poly(ethylene glycol) di(meth)acrylate and/or a mixture thereof, based on the total parts by weight of the core resin equaling 100, having the formula (II): 
xe2x80x83wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) up to 30 parts by weight of a reactive diluent comprising, 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl benzoate, styrene, divinyl benzene or a mixture thereof,
(b) up to 2 parts by weight of an ultraviolet absorber per 100 parts by weight of the core resin; and
(c) up to a combined total of 3 parts by weight of an additive per 100 parts by weight of the core resin.
In the first and second embodiments, the curable composition preferably comprises a core resin mixture wherein (a) component (i) comprises 40-100 parts by weight of (1) the ethoxylated bisphenol A di(meth)acrylate of formula (I) or (2) a mixture of ethoxylated bisphenol A di(meth)acrylates of formula (I), and the average value of n and nxe2x80x2 independently are 0-30, and (b) component (ii) comprises up to 30 parts by weight of the composition of (ii) the poly(ethylene glycol) di(meth)acrylalte of formula (II) and the average value of m is 1 or more.
Preferably, the curable composition of these embodiments comprises a core resin mixture wherein (a) component (i) comprises at least 40 parts by weight of the ethoxylated bisphenol A di(meth)acrylate of formula (I), and n and n are at least 1, and (b) component (ii) comprises 5-30 parts by weight of the poly(ethylene glycol) di(meth)acrylate of formula (II), in which the average value of m is at least 2.
More preferably, the curable composition of these embodiments comprises a core resin mixture wherein (a) component (i) comprises at least 45 parts by weight of the ethoxylated bisphenol A di(meth)acrylate of formula (I), and n and nxe2x80x2 are at least 1, and (b) component (ii) comprises 10-25 parts by weight of the poly(ethylene glycol) di(meth)acrylate of formula (II), and the average volume of m is 3 or more.
Most preferably, the curable composition of these embodiments comprise a core resin mixture wherein (a) component (i) comprises at least 45 parts by weight of the ethoxylated bisphenyl A di(meth)acrylate of formula (I), and n and nxe2x80x2 are 1, and (b) component (ii) comprises 15-25 parts by weight of the poly(ethylene glycol) di(meth)acrylate of formula (II) and the average value of m is 4 or more.
In a third embodiment, the high refractive index curable composition comprises:
(a) a core resin comprising
(i) 40-100 parts by weight of the composition of a first compound and/or a mixture thereof having the formula (I): 
xe2x80x83wherein the average value n and nxe2x80x2 independently are 0-30, R1-R4 independently represent H or C1-C6 alkyl, X is O, S, SO2, CO2, CH2, CHxe2x95x90CH, C(CH3)2 or a single bond, and y,-y, independently represent H, OH, halogen, mercaptan or C1-C4 alkyl,
(ii) up to 30 parts by weight of a second compound of a poly(ethylene glycol) dimethacrylate, based on the total parts by weight of the core resin equaling 100,
wherein the average value of m is 1 or more, R5-R7 independently represent H or C1-C6 alkyl, and
(iii) up to 30 parts by weight of a reactive diluent comprising, 1,6-hexaniediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl benzoate, styrene, divinyl benzene or a mixture thereof,
(b) up to 2 parts by weight of an ultraviolet absorber per 100 parts by weight of the core resin; and
(c) up to a combined total of 3 parts by weight of an additive per 100 parts by weight of the core resin.
The high index curable composition of this invention having a core resin (component (a)), a WV absorber (component (b)) and other additives (component (c)) therein preferably comprises a core resin (component (a)) comprising from about 40 to about 100 parts by weight of the ethoxylated bisphenol A di(meth)acrylate of formula (I) (component (i)) and from about 15 to about 25 parts by weight of poly(ethylene glycol) di(meth)acrylate (component (ii)), based on the total parts by weight of the core resin equaling 100.
In the third embodiment, component (i) of the core resin preferably comprises at least 40 parts by weight of the core resin of (1) the ethoxylated bisphenol A di(meth)acrylate of formula (I), the average value of each and n and nxe2x80x2 independently is at least 1 or (2) a mixture of ethoxylated bisphenol A di(meth)acrylates of formula (I), and 5-30 parts by weight of the composition of the poly(ethylene glycol) di(meth)acrylate of formula II and the average value of m is at least 2.
More preferred for this third embodiment, component (i) of the core resin comprises at least 45 parts by weight of the core resin of the ethoxylated bisphenol A di(meth)acrylate of formula (I), and the average value of each n and nxe2x80x2 is at least 1, and 10-25 parts by weight of the composition of the poly(ethylene glycol) di(meth)acrylate of formula (II) and the average value of m is 3 or more.
Most preferred for this third embodiment, component (i) of the core resin comprises at least 45 parts by weight of the core resin of the ethoxylated bisphenol A di(meth)acrylate of formula (I), and the average value of each n and nxe2x80x2 is 1 and 15-25 parts by weight of the poly(ethylene glycol) di(meth)acrylate of formula (II), and the average value of m is 4 or more.
Further, the high index curable resin compositions of this invention may include additional components such as thermal or UV initiators and/or other known additives such as light stabilizers, blue dye, mold release agent, cross-linker, etc. to improve lens property and lens process, such as thermal/mechanical properties, aging behavior and demolding, etc. Moreover, the high index resin compositions are preferably UV curable.
All of the embodiments described above are low viscosity curable resin compositions which may be used to produce lenses having a refractive index of at least 1.52, and preferably of at least 1.55. The cured resin compositions have excellent impact strength and superior thermal/mechanical properties. The embodiment of the high index curable composition having a IN absorber therein has at least 95%, preferably at least 99% inherent INA protection up to 380 nm and 100% inherent UVB protection.
The methacrylate monomer of ethoxylated bisphenol A di(meth)acrylate is preferred over the acrylate monomer. In formula (I), as the number (n, nxe2x80x2,) of ethylene oxide units increases, the impact strength increases; however, the refractive index decreases. Where a mixture of formula I is used, it is preferred, therefore, that the proper balance of (1) ethoxylated bisphenol A di(meth)acrylates of formula (I) having different degrees of ethoxylation and/or (2) poly(ethylene glycol) di(meth)acrylate of formula (II) with proper m and/or its mixture be achieved to maintain high impact and high refractive index.
The core resin preferably comprises up to 30 parts by weight of reactive diluent, preferably a higher refractive index (RI greater than 1.51) reactive diluent. Preferably, the core resin comprises 5-25 parts by weight of reactive diluent per hundred parts core resin. High refractive index reactive diluents are preferably introduced to raise the overall refractive index and to adjust the overall properties of the casting resin composition.
The reactive diluents useful in the high index casting resin compositions of this invention include 1,6-hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, tri(meth)acrylate, isobornyl (meth)acrylate, 2-hydroxyethyl(meth)acrylate, 2-phenoxyethyl(meth)acrylate, vinyl benzoate, vinyl 4-t-butyl benzoate, styrene, divinyl benzene and mixtures thereof. The more preferred reactive diluents are vinyl benzoate, vinyl t-butyl benzoate, styrene, and mixtures thereof. The most preferred reactive diluent for this composition is 2-phenoxyethyl(meth)acrylate.
UV absorbers can be used to impart inherent UV protection to the high index curable casting resin compositions of this invention. The high refractive index composition of this invention preferably comprises up to 2 parts by weight of UV absorber per 100 weight parts of the core resin composition. More preferably, the composition comprises up to 0.5 parts by weight of UV absorber per 100 weight parts of the core resin. Preferred UV absorbers are benzotrizole derivatives, including but not limited to TINUVIN 328, TINUVIN 384, TINUVIN 900, TINUVIN 1130 and TINUVIN 400, manufactured by Ciba-Geigy of Hawthorne, N.Y. TINUVIN 328 is the more preferred UV absorber. Chemically, TINUVIN 328 is 2-(3xe2x80x2,5xe2x80x2-bis(1,1-dimethylpropyl)-2xe2x80x2-hydroxyphenyl)-2H-benzotriazole.
Up to 2 parts by weight of a UV initiator per 100 parts by weight of core resin may be used in the composition. Preferably, 0.1-1.5 parts by weight of UV initiator is used based on the weight of the core resin. UV initiators which are useful in the composition include, but are not limited to, benzophenone, 2,2-dimethoxy-2-phenyl acetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one, 2-hydroxy-2-methyl-1-phenyl-propan-1-one, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide and mixtures thereof.
Preferred UV initiators include, but are not limited to, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, 2-hydroxy-2-methyl-1-phenyl-propan-1-one and 1-hydroxycyclohexyl phenyl ketone and mixtures thereof. A more preferred UV initiator comprises the mixture of 2,4,6-trimethylbenzoyl diphenylphosphine oxide and 2-hydroxy-2-methyl-1-phenyl-propan-1-one, most preferably by the weight ratio of 1/9-9/1.
The initiator in the composition may also be a mixture of UV and thermal initiators. Thermal initiators which are useful in the composition include, but are not limited to, t-amyl peroxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate, t-butyl peroxyl-2-methylbenzoate, 1,1-di-(t-butylperoxy)-3,3,5-trimethylcyclohexane, t-btutyl peroxy-3,5,5-trimethylhexanoate, t-butylperoxy 2-ethylhexyl carbonate, dibenzoyL peroxide, t-amyl peroxybenzoate and mixtures thereof.
Preferred thermal initiators include, but are not limited to, t-amyl peroxy-2-ethylhexanoate, t-butyl peroxy-2-ethylhexanoate, t-butyl peroxy-3,5,5-trimethylhexanoate and mixtures thereof. In one particular embodiment, the composition comprises 0.1-1.5 and 0.01-1.0 parts, and more preferably, 0.1-1.0 and 0.01-0.5 parts by weight of a mixture of UV and thermal initiators, per 100 parts by weight of the core resin, respectively.
A light stabilizer may be present in the composition of this invention. Preferably, up to 1.0 part by weight of a light stabilizer per 100 parts by weight of the core resin may be used. Preferred light stabilizers include, but are not limited to, TINUVIN 123, TINUVIN 292 AND TINUVIN 144, also manufactured by Ciba-Geigy Corp. of Hawthorne, N.Y. The most preferred light stabilizer is bis(1,2,2,6,6-pentamethyl-4-piperidinyl)sebacate. They do not act by absorbing UV light, but rather by scavenging free radicals. The UV absorber also acts as a light stabilizer to slow down the degradation caused by UV radiation.
Any multifunctional (meth)acrylate can serve as a crosslinker to improve the thermal/mechanical stability. A representative crosslinker is trimethylol propane tri(meth)acrylate.
Some advantageous features of preferred compositions of the present invention are:
1. The viscosity of compositions is very low so that it can be easily processed in the filling stage;
2. The compositions can be cured in 15 min or less with proper UV exposure;
3. The cured lens substrates having a UV absorber therein provide at least 99% inherent UVA up to 380 nm and 100% VB blockage so that no secondary TV treatment and its related processes are required; and/or;
4. The cured lenses exhibit a refractive index of 1.55, excellent impact, resistance and very good thermal/mechanical properties.
The viscosity of the compositions of this invention is preferably less than 1000 cps, and more preferably is less than 400 cps, at ambient temperature (22xc2x0-24xc2x0 C).
The additives for the compositions of this invention preferably comprise a UV absorber for promoting UV protection and/or a stabilizer for long term stability of the cured materials. Preferably, the composition comprises up to 2 parts by weight of a UV absorber per 100 parts by weight of the core resin and up to a total of 2 parts by weight of combined initiators per 100 parts by weight of the core resin. The initiators may be UV and/or thermal.
Having inherent UV protection in the cured lenses of the present invention eliminates the need for typical UV tinting and related process steps. As such, the lens manufacture cycle time and the cost of manufacture can be dramatically reduced.
In a further aspect of the present invention, a polymeric article is formed from a composition as described above. The polymeric article may be a lens or other optical article. The optical article may provide characteristics equal to or greater than those achievable with articles made from previously known formulations, but with a considerably reduced cure time, substantially increased throughput, excellent impact resistance and inherent UV protection. The optical article may be further characterized by having an increased refractive index without degrading other important lens physical properties such as density, impact resistance, color and rigidity (hardness and heat resistance).
The overall refractive index of optical articles produced from the composition of the present invention are preferably from approximately 1.51 to 1.57, more preferably 1.53 to 1.56. The optical articles produced from the compositions of this invention include, but are not limited to lenses, prisms and video disks.
An article is produced according to this invention by processing and curing a composition of this invention. In one embodiment, a glass mold is filled with a composition as described herein and the composition is exposed to a radiation source while in the mold to cure the composition and form a cured article. The cured article is removed from the mold and the cured article is annealed. Preferably, the article is a lens. Preferably, the radiation source provides UV radiation for curing the composition. The radiation source may be a grid, mercury, xenon or any other appropriate actinic radiation source.